Reference Document - RAL25/0020 & OPW25/0194 (As Published)

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6. Comments

6.1    Trafficability

The field work for this investigation was carried out using a 4WD ute mounted drilling rig. At the
time of the investigation the site was trafficable for the drill rig.

The trafficability conditions across the site should not be underestimated particularly during and
following periods of prolonged rainfall. Following periods of wet weather, it is expected that
moisture will tend to be perched in the upper silt/sand material above any shallow clays and may
temporarily rise close to the ground surface. It should be noted that the sandy silt/silty sand
material in overly moist to wet conditions are sensitive to vibrations or trafficking from heavy
equipment, pumping moisture up to near the surface and subsequently losing strength and
becoming ‘boggy’. These conditions will cause problems with trafficability and workability.

Conditioning of wet sandy silt/silty sand material is typically difficult to achieve particularly during
periods of prolonged and intermittent rainfall events, where the moisture content of the
subsurface soils are continually allowed to be kept saturated from surface infiltration (eg. rain) as
well as subsurface seepage. Drying out using surface and subsurface drains may take
considerable time of favourable weather conditions with little or no rainfall before any positive
effect is achieved. Unfavourable, cooler climatic conditions (eg. winter) will also make the drying
out process more difficult and slower to achieve. Wet material which cannot be reasonably
worked or moisture conditioned would be considered unsuitable and may need to be removed
and spoiled from site.

In areas of high traffic (eg. access tracks, haul roads etc.) or where filling is proposed, significant
works to ‘bridge’ over these weakened soils using overburden gravel material, or rock fill, would
be required if weather conditions are unfavourable.

6.2    Site Preparation and Earthworks

It is recommended that the following site preparation and earthworks procedures be carried out
where the proposed development will consist of any new filling, slab-on-ground and/or pavement
construction:
•     Any ‘uncontrolled’ fill, deleterious, soft, wet or highly compressible material or topsoil material
      rich in organics or root matter should be stripped and removed.
•     Assess the moisture content of the subgrade and adjust (if required) to be within 2% of OMC,
      where OMC is the optimum moisture content at Standard compaction.
•     The stripped surface should be rolled with at least four passes of a minimum 12 tonne
      deadweight roller (or as large as practical), with a final test roll pass accompanied by careful
      visual inspection to detect the presence of any soft or loose spots. Areas demonstrating
      excessive movement under test rolling will be required to be either tyned, dried and
      recompacted or removed and replaced with select fill well compacted in layers. Treatment
      should be to a standard sufficient so that the subgrade passes test rolling and that
      compaction can be achieved in the first layer of filling. The extent of treatment is best
      assessed at the time of construction, but large areas of excavation should not proceed
      without geotechnical advice to assess other options.




Proposed Subdivision                                                                   237894.00.R.001.Rev0
12-14 Gympie Street, Tewantin                                                                 October 2025